Due to the ever increasing industrialization impurities dangerous to the purity and living substance of natural water sources occur more and more frequently and great efforts are made all over the world to prevent and eliminate them. Among the impurities, petroleum products are reckoned with as the most dangerous ones. Different methods and equipment have been developed in order to remove them. They can practically be divided in two groups, considering the operational principles.
One of the groups contains (oil) scrapers operating on the basis of the so called adhesion principle in such a way that while oil adheres to certain structural matters submerged in impure water--which are afterwards taken out--water does not adhere to them. Thus the oil can be recovered by scraping, wiping, and extraction from means having a generally large surface (rotary discs, elevators, bundles of fibres, tussels) made of such structural materials (steel, plastics, etc.).
The other group involves oil and impurity scraping methods of separating the impured surface layer of water. Their common feature is that the space inside the spillway or overflow ring of a tank floating on water is sucked by a pump suitable for sucking the mixture of impurities and water created by a difference in level between two parts of the spillway. The surface layer of water and the impurities, such as oil, floating together with same on the surface runs slowly, i.e. overflows through the spillway i.e. overflow ring. The pump sucks the mixture of oil and water flowing in and continuously maintains the difference in level. The mixture sucked is separated so that oil would e.g. gravitationally be separated. There is also equipment known having a scraping unit serving at the same time as separator. A common disadvantage of all known equipment is that they can be used with full efficiency for still water only, as a fundamental condition of their efficient operation is that there can be only at least a slight speed difference between the equipment and the impure water. Therefore, such equipment is operated in such a way that the impurities in the vicinity of the scraper are locally stopped by damming, air blast etc. Scraping, however, is in such case of very low efficiency, considerable losses occur, i.e. depending on the water rate under the effect of the sucking swirls produced, one part of the impurities floating on the surface (such as oil) leaves the scraper, bypassing the equipment and the damming elements mostly from below.